Polymerization of ethylenically unsaturated monomers, such as vinyl chloride, is often carried out in aqueous suspensions and is initiated by thermal decomposition of monomer soluble, free-radical forming compounds, for example organic peroxides or azo compounds. It is often advantageous to charge the initiator in the form of an aqueous suspension comprising small particles of solid initiator.
Peroxide suspensions for the production of PVC is for example disclosed in "PVC-Herstellung unter Anwendung yon Peroxid-Suspensionen", W. F. Verhelst et al, Kunststoffe 70 (1980) 4, pages 224-228. Peroxide suspensions, their preparation and composition, are also disclosed in several patents. GB patent 2068009 describes an aqueous suspension of a solid free-radical forming initiator which suspension comprises different nonionic emulsifiers. EP patent 106627 describes a process for the preparation of an aqueous suspension of a solid organic peroxide which process comprises mixing of the peroxide, a protective colloid, a surface active agent and water at a temperature above the melting point of the peroxide.
The main requirements for initiator suspensions are that they should be easy to handle and sufficiently storage stable and further that they should not have a negative influence on the polymerization processes or on the produced polymerizates. It is further important that the actual process for the preparation of the suspension does not have a detrimental influence on the content of active initiator.